4-Imino-3,4-dihydro-2H-pyrimido[2,1-b][1,3]benzothiazole-2-one (3) was synthesized by the reaction of 2-aminobenzothiazole with ethyl cyanoacetate in solvent free conditions at 150 A degrees C. A series of pyrimido benzothiazole-based azo dyes 4(a-m) were obtained by the coupling of carbocyclic amine-based diazonium chloride with compound (3). The synthesized dyes were purified and characterized by elemental analysis, FT-IR, H-1 NMR, and high-resolution mass spectral data. The solvatochromic behaviors of dyes in various solvents were examined. All the azo dyes exhibited pronounced in vitro antibacterial activities against Gram-positive and Gram-negative bacteria, as well as fungi. The results revealed that most of the compounds exhibited good levels of antibacterial activity. Compounds 4d and 4h showed excellent levels of antimicrobial activity with MIC values of 8.25 mu g/mL.